This invention relates to a short detector and particularly to such a detector which detects shorts between adjacent guide paths. The desire for factory automation has encouraged the widespread use of automatic guided vehicles (AGVs) with self contained motive control systems which travel unattended through aisles in a factory for material delivery. Often the guidance control consists of signal bearing wires buried in the floor along the desired AGV path. A slot or groove in the floor containing the wires is filled with grout to protect the wire. Each wire or guide path carries current at a specified frequency and each AGV has receivers attuned to a given frequency for delivering position signals to its motive control system. The AGV then follows the route of a guide path having the frequency which matches the given frequency of the AGV. If more than one AGV travels the same aisle, two or more routes may coincide. It is then desirable to lay the wires in the same slot. Each wire carries a different frequency so that each AGV can follow its respective guide path and ignore the others.
Experience with such systems has shown that from time to time a sharp piece of metal such as a screw may fall on the floor, become embedded in the grout and contact the guide path wiring. Where two adjacent wires are contacted by the metal intrusion, the wires are shorted and the signal from one guide path can enter another guide path. In that case, a current of a certain frequency may divide and follow two paths so that guide path integrity is lost. An AGV attuned to that frequency may follow the wrong path, stop, or exhibit some erratic behavior. This AGV behavior does not necessarily happen as soon as the short occurs, and in fact such behavior will not occur until the vehicle enters a portion of its route which is affected by the short, so that there will be a time delay between the shorting event and any noticeable problem. In any case, the plant operation is eventually interrupted; and since the AGVs are unattended, some additional time may elapse before the condition is noticed. Then maintenance personnel must analyze any unusual events to determine a cause. Once it is known that the path is shorted they must locate and repair the fault. The repair must be made as soon as possible to prevent or minimize production down time. Thus it is important to be made aware of a short as soon as possible. It is also important to know which of several wires are involved in the short condition.
The AGV systems often are equipped with instruments to detect open circuits in the guide paths. However detectors for short conditions were not available prior to this invention.